Can one saya. I'm sure he will willingly share his interesting ideas if he has any.
b. I'm sure he will willingly share his interesting ideas if he has some.
c. I'm sure he will willingly share his interesting ideas if he has them.
?

None of those are incorrect (though 'c' sounds a little peculiar), but they all sound dismissive and patronising because they suggest that it's very unlikely that the person mentioned has any interesting ideas.

Unless that's what you were intentionally going for, it would be better to say: